Motorists who battle congested roadways throughout the Los Angeles Basin are exposed to between two and four times the levels of cancer-causing toxic chemicals found outdoors, a study released Friday said.

Researchers for the South Coast Air Quality Management District concluded in their two-year study that drivers cannot block the fumes by rolling up their windows, but oddly, can find some relief by opening up their car vents.Moreover, motorists trapped in traffic moving less than 25 mph are exposed to more toxic gases than when traffic moves at more than 30 mph, the study said.

Older cars, those made from 1973 to 1983, spew out much higher levels of carbon monoxide, benzene and toluene - all toxic toxic chemicals believed to pose health risks.

Benzene, a known carcinogen linked to leukemia, was found in concentrations four times higher in cars than outdoors, the researchers said.

"Benzene contributes the greatest risk to the basin's commuters," said the study,

It is estimated that Los Angeles Basin residents have a one in 10,000 chance of getting cancer from benzene exposure. Those who commute an average of 90 minutes a day have a 15 percent greater chance of developing cancer due to benzene exposure than non-commuters.

"I don't think anyone should be terrified by these results," said Dr. Barry Wallerstein, director of planning for the AQMD. "But the public should be aware that this study shows they should begin exploring options to commuting such as ride-sharing, working at home or commuting during off-peak hours."

He said the study, involving measurements taken from 140 vehicles during both winter and summer, was the first "comprehensive" look at air toxics found in cars.

The report said that, even assuming a constant level of inspection and maintenance, older vehicles' emission controls and parts deteriorate, causing more emissions to seep into the car and the air.

It also found lead concentrations in vehicles were about 60 percent higher than outdoor levels.

The report, paid for by the U.S. Environmental Protection Agency, called for stepped-up ride-sharing, traffic signal synchronization and staggered work hours - all of which are proposed in the AQMD's long-term clean air plan approved by the district in March.

The 16 pollutants studied were: carbon monoxide, benzene, toluene, xylene, ethylene dibromide, ethylene dichloride, lead, formaldehyde, acetaldehyde, carbon tetrachloride, chloloroform, perchloroethylene, 1,1,1-Trichloroethylene, cadmium, chromium and nickel.